Power output apparatus, hybrid vehicle provided with power output apparatus, and control method of power output apparatus

INCORPORATION BY REFERENCE

p-0002The disclosure of Japanese Patent Application No. 2009-090331 filed on Apr. 2, 2009 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

p-00031. Field of the Invention

p-0004The invention relates to a power output apparatus, a hybrid vehicle provided with that power output apparatus, and a control method of a power output apparatus.

p-00052. Description of the Related Art

p-0006Japanese Patent Application Publication No. 2004-340102 (JP-A-2004-340102), for example, describes a power output apparatus that includes an internal combustion engine, a planetary gear set that has a planetary carrier connected to a crankshaft of the internal combustion engine, a first electric motor that generates electric power and is connected to a sun gear of the planetary gear set, a second electric motor that outputs power to a ring gear shaft that serves as a drive shaft and is connected to the ring gear of the planetary gear set, and a battery that supplies and receives power to and from the first electric motor and the second electric motor. With this power output apparatus, a supply of fuel to the internal combustion engine is prohibited from being stopped (i.e., a fuel cut is prohibited) to suppress degradation of a catalyst that purifies the exhaust gas of the internal combustion engine when the temperature of the catalyst is equal to or above a set temperature. If there is a demand to decelerate the drive shaft while a fuel cut is being prohibited, the internal combustion engine is controlled so that the output torque becomes a value of 0, and the rotation speed (also simply referred to as “speed” in this specification) of the internal combustion engine is maintained at the value at that time by the first electric motor, while the second electric motor is controlled to output regenerative braking force. Also, Japanese Patent Application Publication No. 2007-084034 (JP-A-2007-084034), for example, describes this type of power output apparatus. When the brake pedal is depressed while a catalyst degradation suppression flag is set to a value of 1 such that a request is being made to suppress catalyst degradation, the described power output apparatus first controls a motor (i.e., the first electric motor) to decrease the speed of the internal combustion engine to a predetermined target speed (such as 800 to 1000 rpm) while the internal combustion engine continues to fire, and then the internal combustion engine is operated on its own.

p-0007Like the technology described in JP-A-2004-340102, having the first electric motor maintain or increase the speed of the internal combustion engine when there is a demand to decelerate the drive shaft while a fuel cut is being prohibited in order to suppress catalyst degradation enables braking force from the so-called engine brake to be output to the drive shaft. It is also possible to inhibit the battery from being overcharged by the electric power regenerated by the second electric motor because the first electric motor consumes electric power. However, if the speed of the internal combustion engine is maintained even though there is a demand for deceleration, it may feel odd to an occupant of the vehicle provided with the power output apparatus. Therefore, if there is a demand to decelerate the drive shaft while a fuel cut is being prohibited to suppress catalyst degradation, the first electric motor is preferably controlled to reduce the speed of the internal combustion engine, like the technology described in JP-A-2007-084034. However, when decreasing the speed of the internal combustion engine, the first electric motor functions as a generator and generates electric power. Therefore, when the amount of electric power that is allowed to be charged to the battery is being limited due to the state of the battery, it becomes necessary to prohibit the speed of the internal combustion engine from being reduced using the first electric motor in order to suppress battery degradation due to overcharging. And if the speed of the internal combustion engine is no longer able to be reduced using the first electric motor in this way, the speed of the internal combustion engine will not quickly decrease even though there is a demand for deceleration, which may feel odd to the occupant of the vehicle provided with the power output apparatus.

SUMMARY OF THE INVENTION

p-0008Therefore, the power output apparatus, the hybrid vehicle provided with that power output apparatus, and the control method of the power output apparatus of the invention quickly reduce the speed of an internal combustion engine when there is a demand to decelerate a drive shaft while a supply of fuel to the internal combustion engine is prohibited from being stopped in order to suppress catalyst degradation.

p-0009A first aspect of the invention relates to a power output apparatus that outputs power to a drive shaft. This power output apparatus includes an internal combustion engine; an exhaust gas control apparatus that includes a catalyst for purifying exhaust gas discharged from the internal combustion engine; a first electric motor that inputs and outputs power; a power distributing portion that is connected to three shafts, including an engine shaft of the internal combustion engine, a rotating shaft of the first electric motor, and the drive shaft, and inputs and outputs power that is based on power input and output from and to two of these three shafts, to and from the remaining shaft; a second electric motor that inputs and outputs power from and to the drive shaft; a power storage device that supplies and receives electric power to and from the first electric motor and the second electric motor; a required torque setting portion that sets a required torque that is required at the drive shaft; and a control portion that, when there is a demand to decelerate the drive shaft while a supply of fuel to the internal combustion engine is being prohibited to suppress degradation of the catalyst, controls the internal combustion engine, the first electric motor, and the second electric motor such that torque based on the set required torque is output to the drive shaft and the rotation speed of the internal combustion engine is decreased to a preset self-sustaining rotation speed with the supply of fuel and an intake air adjustment that increases the intake air amount of the internal combustion engine as the temperature of the power storage device increases.

p-0010With the power output apparatus according to this first example embodiment, when there is a demand to decelerate the drive shaft while a supply of fuel to the internal combustion engine is being prohibited to suppress degradation of the catalyst, the internal combustion engine, the first electric motor, and the second electric motor are controlled such that torque based on the set required torque is output to the drive shaft and the rotation speed of the internal combustion engine is decreased to a preset self-sustaining rotation speed with the supply of fuel and an intake air adjustment that increases the intake air amount of the internal combustion engine as the temperature of the power storage device increases. By executing the intake air adjustment that increases the intake air amount of the internal combustion engine as the temperature of the power storage device increases when there is a demand to decelerate the drive shaft while a supply of fuel to the internal combustion engine is being prohibited to suppress degradation of the catalyst in this way, even if the rotation speed of the internal combustion engine stops being decreased by the first electric motor taking into account the fact that the temperature of the power storage device is relatively high such that the power that is allowed to be charged is limited, it is still possible to promote a decrease in the rotation speed of the internal combustion engine by increasing the friction by adjusting the intake air amount. Therefore, with the power output apparatus according to this aspect, the rotation speed of the internal combustion engine can be quickly decreased regardless of the state of the power storage device, when there is a demand to decelerate the drive shaft while a supply of fuel to the internal combustion engine is being prohibited to suppress degradation of the catalyst.

p-0011A second aspect of the invention relates to a hybrid vehicle that includes the power output apparatus according to the first aspect described above, and a driving wheel that is connected to the drive shaft. With the hybrid vehicle according to this second aspect, the rotation speed of the internal combustion engine can be quickly decreased regardless of the state of the power storage device, when there is a demand to decelerate the drive shaft while a supply of fuel to the internal combustion engine is being prohibited to suppress degradation of the catalyst.

p-0012A third aspect of the invention relates to a control method of a power output apparatus provided with an internal combustion engine, an exhaust gas control apparatus that includes a catalyst for purifying exhaust gas discharged from the internal combustion engine, a first electric motor that inputs and outputs power, a power distributing portion that is connected to three shafts, including an engine shaft of the internal combustion engine, a rotating shaft of the first electric motor, and the drive shaft, and inputs and outputs power that is based on power input and output from and to two of these three shafts, from and to the remaining shaft, a second electric motor that inputs and outputs power from and to the drive shaft, and a power storage device that supplies and receives electric power to and from the first electric motor and the second electric motor. This control method includes controlling, when there is a demand to decelerate the drive shaft while a supply of fuel to the internal combustion engine is being prohibited to suppress degradation of the catalyst, the internal combustion engine, the first electric motor, and the second electric motor such that torque based on a required torque that is required at the drive shaft is output to the drive shaft and the rotation speed of the internal combustion engine is decreased to a preset self-sustaining rotation speed with the supply of fuel and an intake air adjustment that increases the intake air amount of the internal combustion engine as the temperature of the power storage device increases.

p-0013According to the control method of a power output apparatus according to this third aspect, the rotation speed of the internal combustion engine can be quickly decreased regardless of the state of the power storage device, when there is a demand to decelerate the drive shaft while a supply of fuel to the internal combustion engine is being prohibited to suppress degradation of the catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS

p-0014The foregoing and/or further objects, features and advantages of the invention will become more apparent from the following description of example embodiments with reference to the accompanying drawings, in which like numerals are used to represent like elements and wherein:

p-0015<figref idrefs="DRAWINGS">FIG. 1</figref> is a block diagram schematically showing a hybrid vehicle according to a first example embodiment of the invention;

p-0016<figref idrefs="DRAWINGS">FIG. 2</figref> is a block diagram schematically showing an engine according to the first example embodiment of the invention;

p-0017<figref idrefs="DRAWINGS">FIG. 3</figref> is a graph showing an example of a relationship between battery temperature and input and output limits of a battery according to the first example embodiment of the invention;

p-0018<figref idrefs="DRAWINGS">FIG. 4</figref> is a graph showing an example of a relationship between state-of-charge (SOC) of the battery and correction coefficients of the input and output limits according to the first example embodiment of the invention;

p-0019<figref idrefs="DRAWINGS">FIG. 5</figref> is a flowchart illustrating an example of an accelerator-off drive control routine that is executed by a hybrid ECU according to the first example embodiment of the invention;

p-0020<figref idrefs="DRAWINGS">FIG. 6</figref> is a view of an example of a required torque setting map according to the first example embodiment of the invention;

p-0021<figref idrefs="DRAWINGS">FIG. 7</figref> is a view of an example of a target throttle opening amount setting map according to the first example embodiment of the invention;

p-0022<figref idrefs="DRAWINGS">FIG. 8</figref> is a view of an example of an alignment graph that shows the dynamic relationship between rotation speed and torque of rotating elements in a power splitting/combining device according to the first example embodiment of the invention;

p-0023<figref idrefs="DRAWINGS">FIG. 9</figref> is a view of another example of a target throttle opening amount setting map according to the first example embodiment of the invention;

p-0024<figref idrefs="DRAWINGS">FIG. 10</figref> is a block diagram schematically showing a hybrid vehicle according to a second example embodiment of the invention; and

p-0025<figref idrefs="DRAWINGS">FIG. 11</figref> is a block diagram schematically showing a hybrid vehicle according to a third example embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

p-0026<figref idrefs="DRAWINGS">FIG. 1</figref> is a block diagram schematically showing a hybrid vehicle <b>20</b> according to a first example embodiment of the invention. The hybrid vehicle <b>20</b> shown in the drawing is provided with an engine <b>22</b>, a three shaft-type power splitting/combining device <b>30</b> that is connected via a damper <b>28</b> to a crankshaft (an engine shaft) <b>26</b> of the engine <b>22</b>, a motor MG<b>1</b> that is able to generate power and is connected to the power splitting/combining device <b>30</b>, a reduction gear <b>35</b> that is connected to a ring gear shaft <b>32</b><i>a </i>that serves as a drive shaft and is connected to the power splitting/combining device <b>30</b>, a motor MG<b>2</b> that is connected to the ring gear shaft <b>32</b><i>a </i>via this reduction gear <b>35</b>, and a hybrid electronic control unit (hereinafter, simply referred to as “hybrid ECU”) <b>70</b> that controls the overall hybrid vehicle <b>20</b>, and the like.

p-0027The engine <b>22</b> is an internal combustion engine that outputs power by combusting a mixture of a hydrocarbon fuel, such as gasoline or light oil, and air inside a combustion chamber <b>120</b>, and converting the reciprocating motion of a piston <b>121</b> that results from the combustion of the air-fuel mixture into rotary motion of the crankshaft <b>26</b>. In this engine <b>22</b>, air that has been cleaned by an air-cleaner <b>122</b> is drawn into an intake pipe <b>126</b> via a throttle valve <b>123</b>, and fuel such as gasoline is injected from a fuel injection valve <b>127</b> into this intake air, as is evident from <figref idrefs="DRAWINGS">FIG. 2</figref>. The thus obtained air-fuel mixture is then drawn into the combustion chamber <b>120</b> via an intake valve <b>131</b> that is driven by a valve mechanism <b>130</b> structured as a variable valve timing mechanism, and ignited by an electric spark from a spark plug <b>128</b> so that it combusts. Exhaust gas from the engine <b>22</b> is delivered via an exhaust valve <b>132</b> and an exhaust manifold <b>140</b> to an exhaust gas control apparatus <b>141</b> that includes an exhaust gas control catalyst (i.e., a three-way catalyst) <b>141</b><i>c </i>that purifies harmful components such as carbon monoxide (CO), hydrocarbons (HC), and oxides of nitrogen (NOx). After being purified by the exhaust gas control apparatus <b>141</b>, the exhaust gas is discharged outside. Also, the engine <b>22</b> includes an EGR passage <b>142</b> that is connected to the exhaust passage downstream of the exhaust gas control apparatus <b>141</b> and circulates exhaust gas to a surge tank (i.e., the intake system), an EGR valve <b>143</b> that is provided midway in this EGR passage <b>142</b> and regulates the recirculation amount (i.e., the EGR amount) of exhaust gas (i.e., EGR gas) that is circulated from the exhaust system to the intake system, and a temperature sensor <b>144</b> that detects the temperature of the EGR gas inside the EGR passage <b>142</b>, and the like.

p-0028The engine <b>22</b> structured in this way is controlled by an engine electronic control unit (hereinafter, simply referred to as an “engine ECU”) <b>24</b>. As shown in <figref idrefs="DRAWINGS">FIG. 2</figref>, the engine ECU <b>24</b> is formed as a microprocessor that is centered around a CPU <b>24</b><i>a</i>, and includes, in addition to the CPU <b>24</b><i>a</i>, ROM <b>24</b><i>b </i>that stores various processing programs, RAM <b>24</b><i>c </i>that temporarily stores data, and input/output ports and a communication port, not shown, and the like. Signals from various sensors that detect the state of the engine <b>22</b> and the like are input to the engine ECU <b>24</b> via the input port, not shown. Some examples of these signals include a signal indicative of the crank position from a crank position sensor <b>180</b> that detects the rotational position of the crankshaft <b>26</b>, a signal indicative of the coolant temperature Tw from a coolant temperature sensor <b>181</b> that detects the temperature of the coolant of the engine <b>22</b>, a signal indicative of the cylinder pressure from a cylinder pressure sensor <b>182</b> that detects the pressure inside the combustion chamber <b>120</b>, a signal indicative of the cam position from a cam position sensor <b>133</b> that detects the rotational position of a camshaft included in the valve mechanism <b>130</b> that drives the intake valve <b>131</b> and the exhaust valve <b>132</b>, and a signal indicative of the throttle position from a throttle valve position sensor <b>124</b> that detects the position of the throttle valve <b>123</b>. Other examples of signals that are input to the engine ECU <b>24</b> via the input port include a signal indicative of the intake air amount GA from an airflow meter <b>183</b> that detects the intake air amount as the load of the engine <b>22</b>, a signal indicative of the intake air temperature Tair from an intake air temperature sensor <b>184</b> provided in the intake passage <b>126</b>, a signal indicative of an intake air negative pressure Pi from an intake air pressure sensor <b>185</b> that detects negative pressure in the intake passage <b>126</b>, a signal indicative of the air-fuel ratio AF from an air-fuel ratio sensor <b>186</b> arranged upstream of the exhaust gas control apparatus <b>141</b> in the exhaust manifold <b>140</b>, a signal indicative of the catalyst bed temperature Tcat from a catalyst temperature sensor <b>187</b> that detects the temperature of the catalyst bed of the exhaust gas control apparatus <b>141</b> (i.e., the temperature of the exhaust gas control catalyst <b>141</b><i>c</i>), and a signal indicative of the EGR gas temperature from a temperature sensor <b>144</b> in the EGR passage <b>142</b>. Also, various control signals for driving the engine <b>22</b> are output via the output port, not shown. Some examples of control signals output from the engine ECU <b>24</b> via the output port include a drive signal to a throttle motor <b>125</b> that adjusts the position of the throttle valve <b>123</b>, a drive signal to a fuel injection valve <b>127</b>, a control signal to an ignition coil <b>129</b> that is integrated with an igniter, a control signal to the valve mechanism <b>130</b>, and a drive signal to the EGR valve <b>143</b>. Also, the engine ECU <b>24</b> calculates the speed Ne of the engine <b>22</b> using the crank position from the crank position sensor <b>180</b>. Further, the engine ECU <b>24</b> communicates with the hybrid ECU <b>70</b> and controls the operation of the engine <b>22</b> according to the control signals from the hybrid ECU <b>70</b>, as well as outputs data related to the operating state of the engine <b>22</b> to the hybrid ECU <b>70</b> as necessary.

p-0029The power splitting/combining device <b>30</b> is a single pinion type planetary gear set that has a sun gear <b>31</b> that is a gear with external teeth, a ring gear <b>32</b> that is a gear with internal teeth that is arranged concentric with the sun gear <b>31</b>, and a carrier <b>34</b> that pivotally and rotatably retains a plurality of pinion gears <b>33</b> that are in mesh with both the sun gear <b>31</b> and the ring gear <b>32</b>, with these three elements, i.e., the sun gear <b>31</b>, the ring gear <b>32</b>, and the carrier <b>34</b>, being able to differentially rotate with respect to one another. A rotating shaft of the motor MG<b>1</b> is connected to the sun gear <b>31</b> that is the first element of the power splitting/combining device <b>30</b>, the crankshaft <b>26</b> of the engine <b>22</b> is connected to the carrier <b>34</b> which is the second element, and a rotating shaft of the motor MG<b>2</b> is connected to the ring gear <b>32</b> which is the third element via the reduction gear <b>35</b> and the ring gear shaft <b>32</b><i>a </i>that serves as the drive shaft. When the motor MG<b>1</b> functions as a generator, the power splitting/combining mechanism <b>30</b> distributes the power from the engine <b>22</b> that is input from the carrier <b>34</b> to the sun gear <b>31</b> side and the ring gear <b>32</b> side according to the gear ratio of the sun gear <b>31</b> and the ring gear <b>32</b>. When the motor MG<b>1</b> functions as a motor, the power splitting/combining mechanism <b>30</b> combines the power from the engine <b>22</b> that is input from the carrier <b>34</b> with the power from the motor MG<b>1</b> that is input from the sun gear <b>31</b>, and outputs the combined power to the ring gear <b>32</b> side. The power output to the ring gear <b>32</b> is ultimately output from the ring gear shaft <b>32</b><i>a </i>to wheels <b>39</b><i>a </i>and <b>39</b><i>b</i>, which are driving wheels, via a gear mechanism <b>37</b> and a differential gear <b>38</b>.

p-0030The motors MG<b>1</b> and MG<b>2</b> are structured as well-known synchronous motor-generators capable of operating as both a generator and a motor, and supply and receive electric power to and from a battery <b>50</b>, which is a secondary battery, via inverters <b>41</b> and <b>42</b>, respectively. A power line <b>54</b> that connects the inverters <b>41</b> and <b>42</b> to the battery <b>50</b> is structured as a positive bus and a negative bus shared by both of the inverters <b>41</b> and <b>42</b>, such that electric power generated by one motor (either the MG<b>1</b> or the MG<b>2</b>) can be consumed by the other motor. Therefore, the battery <b>50</b> is charged by electric power generated by the motor MG<b>1</b> or MG<b>2</b> and discharged if the electric power of the motor MG<b>1</b> or MG<b>2</b> is insufficient. If the electric power from the motors MG<b>1</b> and MG<b>2</b> is balanced, the battery <b>50</b> will neither be charged nor discharged. Both of the motors MG<b>1</b> and MG<b>2</b> are drivingly controlled by a motor electronic control unit (hereinafter, simply referred to as a “motor ECU”) <b>40</b>. This motor ECU <b>40</b> receives signals necessary for drivingly controlling the motors MG<b>1</b> and MG<b>2</b>, such as signals from rotational position detecting sensors <b>43</b> and <b>44</b> that detect the rotational position of the rotors of the motors MG<b>1</b> and MG<b>2</b>, and the phase current applied to the motors MG<b>1</b> and MG<b>2</b> that is detected by current sensors, not shown, and the like. The motor ECU <b>40</b> outputs switching control signals to the inverters <b>41</b> and <b>42</b>, and the like. The motor ECU <b>40</b> also executes a rotation speed calculating routine, not shown, based on the signals received from the rotational position detecting sensors <b>43</b> and <b>44</b>, and calculates the rotation speeds Nm<b>1</b> and Nm<b>2</b> of the rotors of the motors MG<b>1</b> and MG<b>2</b>. Further, the motor ECU <b>40</b> communicates with the hybrid ECU <b>70</b> and drivingly controls the motors MG<b>1</b> and MG<b>2</b> based on control signals and the like from the hybrid ECU <b>70</b>, as well as outputs data related to the operating states of the motors MG<b>1</b> and MG<b>2</b> to the hybrid ECU <b>70</b> when necessary.

p-0031The battery <b>50</b> is structured as a lithium-ion secondary battery or a nickel-metal hydride secondary battery, and is controlled by a battery electronic control unit (hereinafter, simply referred to as a “battery ECU”) <b>52</b>. This battery ECU <b>52</b> receives signals necessary for controlling the battery <b>50</b>, such as a signal indicative of the terminal voltage from a voltage sensor, not shown, arranged between the terminals of the battery <b>50</b>, a signal indicative of the charge-discharge current from a current sensor, not shown, provided in the power line <b>54</b> that is connected to an output terminal of the battery <b>50</b>, and a signal indicative of the battery temperature Tb from a temperature sensor <b>51</b> mounted to the battery <b>50</b>, and the like. The battery ECU <b>52</b> communicates with the hybrid ECU <b>70</b> and outputs data related to the state of the battery <b>50</b> to the hybrid ECU <b>70</b> when necessary. Further, to control the battery <b>50</b>, the battery ECU <b>52</b> calculates the state-of-charge (SOC) based on the integrated value of the charge-discharge current detected by the current sensor, calculates the required charge-discharge electric power Pb* of the battery <b>50</b> based on that state-of-charge SOC, and calculates an input limit Win as an allowable charge electric power, which is the amount of electric power allowed to be charged to the battery <b>50</b>, and an output limit Wout as an allowable discharge electric power, which is the amount of electric power allowed to be discharged from the battery <b>50</b>, based on the state-of-charge SOC and the battery temperature Tb. Incidentally, the input and output limits Win and Wout of the battery <b>50</b> are able to be set by first setting basic values for the input and output limits Win and Wout based on the battery temperature Tb, as well as setting an output limit correction coefficient and an input limit correction coefficient based on the state-of-charge SOC of the battery <b>50</b>, and then multiplying the basic value of the set input limit Win by the input limit correction coefficient to obtain the input limit Win, and multiplying the basic value of the set output limit Wout by the output limit correction coefficient to obtain the output limit Wout.

p-0032The hybrid ECU <b>70</b> is formed as a microprocessor that is centered around a CPU <b>72</b>, and includes, in addition to the CPU <b>72</b>, ROM <b>74</b> that stores processing programs, RAM <b>76</b> that temporarily stores data, a timer <b>78</b> that measures time according to a timekeeping command, and input/output ports and a communication port, not shown, and the like. Signals from various sensors are input via the input port to the hybrid ECU <b>70</b>. Some examples of these signals include an ignition signal from an ignition switch (i.e., a start switch) <b>80</b>, a signal indicative of a shift position SP from a shift position sensor <b>82</b> that detects the shift position SP which is the operating position of a shift lever <b>81</b>, a signal indicative of an accelerator operation amount Acc from an accelerator pedal position sensor <b>84</b> that detects the depression amount of an accelerator pedal <b>83</b>, a signal indicative of a brake pedal stroke BS from a brake pedal stroke sensor <b>86</b> that detects the depression amount of a brake pedal <b>85</b>, and a signal indicative of the vehicle speed V from a vehicle speed sensor <b>87</b>, and the like. As described above, the hybrid ECU <b>70</b> is connected to the engine ECU <b>24</b>, the motor ECU <b>40</b>, and the battery ECU <b>52</b> and the like via the communication port, and sends and receives various control signals and data to and from the engine ECU <b>24</b>, the motor ECU <b>40</b>, and the battery ECU <b>52</b> and the like.

p-0033In the hybrid vehicle <b>20</b> structured as described above, the required torque Tr* to be output to the ring gear shaft <b>32</b><i>a </i>that serves as the drive shaft is calculated based on the vehicle speed V and the accelerator operation amount Acc that corresponds to the depression amount of the accelerator pedal <b>83</b> by the driver. The engine <b>22</b> and the motors MG<b>1</b> and MG<b>2</b> are controlled such that torque based on this required torque Tr* is output to the ring gear shaft <b>32</b><i>a</i>. Some examples of operation control modes of the engine <b>22</b> and the motors MG<b>1</b> and MG<b>2</b> are i) a torque converting operating mode, ii) a charge-discharge operating mode, and iii) a motor operating mode. In the torque converting operating mode, the engine <b>22</b> is controlled to output power comparable to the required torque Tr*, and the motors MG<b>1</b> and MG<b>2</b> are controlled to output all of the power output from the engine <b>22</b> to the ring gear shaft <b>32</b><i>a </i>after it has been converted to torque by the power splitting/combining device <b>30</b>, the motor MG<b>1</b>, and the motor MG<b>2</b>. In the charge-discharge operating mode, the engine <b>22</b> is controlled to output power comparable to the sum of the required torque Tr* and the electric power needed to be charged or discharged to or from the battery <b>50</b>, and the motors MG<b>1</b> and MG<b>2</b> are controlled to output torque based on the required torque Tr* to the ring gear shaft <b>32</b><i>a </i>after all or some of the power output from the engine <b>22</b> with the charge-discharge of the battery <b>50</b> is converted to torque by the power splitting/combining device <b>30</b> and the motors MG<b>1</b> and MG<b>2</b>. In the motor operating mode, the engine <b>22</b> is stopped and the motor MG<b>2</b> is controlled to output torque based on the required torque Tr* to the ring gear shaft <b>32</b><i>a</i>. Also, in the hybrid vehicle <b>20</b> of this example embodiment, when a predetermined condition is satisfied in the torque converting operating mode or the charge-discharge operating mode, intermittent operation is executed in which the engine <b>22</b> is automatically stopped and started.

p-0034Furthermore, with the hybrid vehicle <b>20</b> in this first example embodiment, a catalyst degradation suppression determining routine, not shown, is executed by the engine ECU <b>24</b>. If the temperature of the exhaust gas control catalyst <b>141</b><i>c </i>increases such that the catalyst bed temperature Tcat of the exhaust gas control apparatus <b>141</b> becomes equal to or greater than a first temperature, a predetermined catalyst degradation suppression flag Fc is set to a value of 1 until the catalyst bed temperature Tcat falls below a second temperature that is lower than the first temperature. When the catalyst degradation suppression flag Fc is set to a value of 1, a fuel cut in the engine <b>22</b> is prohibited to suppress the catalyst bed temperature from further increasing due to large amounts of air being supplied to the hot exhaust gas control catalyst <b>141</b><i>c</i>, when there is a demand to decelerate the hybrid vehicle <b>20</b> (i.e., the ring gear shaft <b>32</b><i>a</i>) by the driver releasing (i.e., letting up on) the accelerator pedal <b>83</b> or depressing the brake pedal <b>85</b>, so that the catalyst bed temperature will not further increase and degrade the exhaust gas control catalyst <b>141</b><i>c</i>. That is, when the catalyst degradation suppression flag Fc is set to a value of 1, fuel is injected into the combustion chambers <b>120</b> and the air-fuel mixture is ignited even if ordinarily a fuel cut in the engine <b>22</b> should be executed.

p-0035Next, operation of the hybrid vehicle <b>20</b> when the catalyst degradation suppression flag Fc described above is set to a value of 1 will be described. More particularly, operation of the hybrid vehicle <b>20</b> when the driver releases (i.e., lets up on) the accelerator pedal <b>83</b> when the catalyst degradation suppression flag Fc is set to a value of 1 will be described.

p-0036<figref idrefs="DRAWINGS">FIG. 5</figref> is a flowchart of an example of an accelerator-off drive control routine that is executed at predetermined intervals of time (such as every several milliseconds) by the hybrid ECU <b>70</b> of the first example embodiment when the driver releases the accelerator pedal <b>83</b> while the drive position for normal forward running is selected as the shift position. When the routine in <figref idrefs="DRAWINGS">FIG. 5</figref> starts, the CPU <b>72</b> of the hybrid ECU <b>70</b> inputs data necessary for control, such as the vehicle speed V from the vehicle speed sensor <b>87</b>, the speed Ne of the engine <b>22</b>, the rotation speeds Nm<b>1</b> and Nm<b>2</b> of the motors MG<b>1</b> and MG<b>2</b>, the input and output limits Win and Wout of the battery <b>50</b>, the temperature Tb of the battery <b>50</b>, and the value of the catalyst degradation suppression flag Fc (step S<b>100</b>). Here, the speed Ne of the engine <b>22</b> is calculated by the engine ECU <b>24</b> based on the crank position from the crank position sensor <b>180</b> and input to the hybrid ECU <b>70</b> through communication from the engine ECU <b>24</b>. Also, the rotation speeds Nm<b>1</b> and Nm<b>2</b> of the motors MG<b>1</b> and MG<b>2</b> are calculated by the motor ECU <b>40</b> based on the signals from the rotational position detecting sensors <b>43</b> and <b>44</b> and input to the hybrid ECU <b>70</b> through communication from the motor ECU <b>40</b>. Furthermore, the input and output limits Win and Wout and the battery temperature Tb are input to the hybrid ECU <b>70</b> through communication from the battery ECU <b>52</b>. The catalyst degradation suppression flag Fc is input to the hybrid ECU <b>70</b> through communication from the engine ECU <b>24</b>. After the data is input in step S<b>100</b>, it is determined whether the input catalyst degradation suppression flag Fc is a value of 1 (step S<b>110</b>). If the catalyst degradation suppression flag Fc is a value of 0, in which it is regarded that there is no fear of degradation of the exhaust gas control catalyst <b>141</b><i>c</i>, normal accelerator-off control is executed (step S<b>260</b>) and this cycle of the routine ends.

p-0037Also, if it is determined that the catalyst degradation suppression flag Fc is a value of 1 in step S<b>110</b>, the required torque Tr* to be output to the ring gear shaft <b>32</b><i>a </i>is set based on the vehicle speed V input in Step S<b>100</b> (step S<b>120</b>). In this first example embodiment, the relationship between the required torque Tr* and the vehicle speed V when the accelerator is off, i.e., when the accelerator operation amount Acc is a value of 0, is preset and stored in the ROM <b>74</b> in the form of a required torque setting map. A required torque Tr* that corresponds to a given vehicle speed V is derived and set from this map. <figref idrefs="DRAWINGS">FIG. 6</figref> shows one example of a required torque setting map used when the accelerator is off. Next, a target speed Ne* of the engine <b>22</b> is set to a preset self-sustaining speed Nref (step S<b>130</b>). This self-sustaining speed Nref is a speed at which the engine <b>22</b> is operated so that it outputs essentially no torque while fuel continues to be injected into the combustion chambers <b>120</b> and the air-fuel mixture continues to be ignited, after the catalyst degradation suppression flag Fc has been set to a value of 1 and a fuel cut in the engine <b>22</b> has been prohibited. In this first example embodiment, this self-sustaining speed Nref is set to idling speed or a value near there (such as 800 to 1200 rpm, for example).

p-0038Once the target speed Ne* of the engine <b>22</b> is set, it is then determined whether a predetermined flag F is a value of 0 (step S<b>140</b>). If the flag F is a value of 0, it is then determined whether the absolute value of the difference between the speed Ne of the engine <b>22</b> input in step S<b>100</b> and the target speed Ne* is greater than a predetermined value α (such as a value of approximately 50 rpm, for example) (step S<b>150</b>). If the absolute value of the difference between the speed Ne and the target speed Ne* is greater than the predetermined value α, it is then determined whether the battery temperature Tb input in step S<b>100</b> is equal to or lower than a preset reference temperature Tbref (step S<b>160</b>). This reference temperature Tbref is an upper limit temperature when the input limit Win, which is the amount of electric power allowed to be charged to the battery <b>50</b>, is not limited to a small amount of charge electric power by the relationship with the battery temperature Tb. This reference temperature Tbref is set to a value of approximately 40° C., for example. If the battery temperature Tb is equal to or lower than the reference temperature Tbref, a fuel cut prohibiting command to prohibit the injection of fuel into the combustion chambers <b>120</b> from being stopped, i.e., to prohibit a fuel cut, is output to the engine ECU <b>20</b> (step S<b>170</b>). Then, a torque command Tm<b>1</b>* for the motor MG<b>1</b> is set according to Expression (1) below to reduce the speed Ne of the engine <b>22</b> by outputting negative torque from the motor MG<b>1</b> to the crankshaft <b>26</b> (step S<b>180</b>). Here, Expression (1) is a relational expression of feedback control for reducing the speed Ne of the engine <b>22</b> to the target speed Ne* (i.e., the self-sustaining speed Nref) while fuel continues to be supplied to the engine <b>22</b>, i.e., while the engine <b>22</b> continues to fire. In Expression (1), the first term on the right side, k<b>1</b>, is a proportional term of the gain, and the second term on the right side, k<b>2</b>, is an integral term of the gain. These gains k<b>1</b> and k<b>2</b> are set to small values compared with when a relatively large amount of torque is being output from the engine <b>22</b>, because it is necessary to keep the engine <b>22</b> firing. <br /><i>Tm</i>1*=<i>k</i>1×(<i>Ne*−Ne</i>)+<i>k</i>2×∫(<i>Ne*−Ne</i>)<i>dt</i>  (1)

p-0039Continuing on, a target throttle opening amount TH* of the throttle valve <b>123</b> of the engine <b>22</b> is set based on the battery temperature Tb and the speed Ne of the engine <b>22</b> input in step S<b>100</b> (step S<b>190</b>). In this first example embodiment, the relationships among the speed Ne of the engine <b>22</b>, the battery temperature Tb, and the target throttle opening amount TH* are set beforehand and stored in the ROM <b>74</b> in the form of a target throttle opening amount setting map. A target throttle opening amount TH* that corresponds to a given speed Ne and a given battery temperature Tb is derived and set from this map. <figref idrefs="DRAWINGS">FIG. 7</figref> shows an example of a target throttle opening amount setting map. The target throttle opening amount setting map in the first example embodiment defines the target throttle opening amount TH* such that the amount of air that is drawn into the engine <b>22</b> is greater than the amount of intake air required during self-sustained operation at the self-sustaining speed Nref but less than the amount of intake air required when operating under a load at the self-sustaining speed Nref. As shown in <figref idrefs="DRAWINGS">FIG. 7</figref>, the intake air amount tends to be increased as the speed Ne of the engine <b>22</b> increases, and also tends to be increased as the battery temperature Tb increases.

p-0040After step S<b>190</b>, torque limits Tmin and Tmax are calculated according to Expressions (2) and (3), respectively, as upper and lower limits for the torque that may be output from the motor MG<b>2</b>, using the input and output limits Win and Wout of the battery <b>50</b>, the torque command Tm<b>1</b>* for the motor MG<b>1</b> set in step S<b>180</b>, and the current rotation speeds Nm<b>1</b> and Nm<b>2</b> of the motors MG<b>1</b> and MG<b>2</b> (step S<b>200</b>). Moreover, a temporary motor torque Tm<b>2</b>tmp, which is a temporary value of the torque that should be output from the motor MG<b>2</b>, is calculated according to Expression (4) below using the required torque Tr*, the torque command Tm<b>1</b>*, the gear ratio ρ of the power splitting/combining device <b>30</b>, and the gear ratio Gr of the reduction gear <b>35</b> (step S<b>210</b>). Then the torque command Tm<b>2</b>* for the motor MG<b>2</b> is set to a value that the temporary motor torque Tm<b>2</b>tmp is limited to by the torque limits Tmin and Tmax (step S<b>220</b>). Setting the torque command Tm<b>2</b>* for the motor MG<b>2</b> in this way enables the torque that is output to the ring gear shaft <b>32</b><i>a </i>to be limited to within the input and output limits Win and Wout of the battery <b>50</b>. Here, Expression (4) is a dynamic relational expression for the rotating elements of the power splitting/combining device <b>30</b>. <figref idrefs="DRAWINGS">FIG. 8</figref> is an example of an alignment graph that shows the dynamic relationship between rotation speed and torque of the rotating elements in the power splitting/combining device <b>30</b>. In the drawing, the S axis on the left side represents the rotation speed of the sun gear <b>31</b> that matches the rotation speed Nm<b>1</b> of the motor MG<b>1</b>, the C axis in the center represents the rotation speed of the carrier <b>34</b> that matches the speed Ne of the engine <b>22</b>, and the R axis on the right side represents the rotation speed Nr of the ring gear <b>32</b>, which is equal to the rotation speed Nm<b>2</b> of the motor MG<b>2</b> divided by the gear ratio Gr of the reduction gear <b>35</b>. Also, the two bold arrows on the R axis indicate the torque that acts on the ring gear shaft <b>32</b><i>a </i>from the torque output when the torque Tm<b>1</b> is output by the motor MG<b>1</b>, and the torque that acts on the ring gear shaft <b>32</b><i>a </i>via the reduction gear <b>35</b> when the torque Tm<b>2</b> is output by the motor MG<b>2</b>. Expression (4) for obtaining the temporary motor torque Tm<b>2</b>tmp can be derived easily using the relationships of the rotation speeds in this alignment graph. Once the target speed Ne* and target throttle opening amount TH* of the engine <b>22</b> and the torque commands Tm<b>1</b>* and Tm<b>2</b>* for the motors MG<b>1</b> and MG<b>2</b> have been set in this way, the target speed Ne* and the target throttle opening amount TH* are output to the engine ECU <b>24</b>, and the torque commands Tm<b>1</b>* and Tm<b>2</b>* for the motors MG<b>1</b> and MG<b>2</b> are output to the motor ECU <b>40</b> (step S<b>230</b>). Then this cycle of the routine ends. <br /><i>T</i>min=(<i>W</i>in−<i>Tm</i>1*×<i>Nm</i>1)/<i>Nm</i>2  (2)<br /><i>T</i>max=(<i>W</i>out−<i>Tm</i>1*×<i>Nm</i>1)/<i>Nm</i>2  (3)<br /><i>Tm</i>2<i>tmp</i>=(<i>Tr*+Tm</i>1*/ρ)/<i>Gr</i>  (4)

p-0041After receiving the fuel cut command, the target speed Ne*, and the target throttle opening amount TH* from the hybrid ECU <b>70</b>, the engine ECU <b>24</b> controls the throttle motor <b>125</b> based on the throttle position obtained by the throttle valve position sensor <b>124</b>, so that the opening amount of the throttle valve <b>123</b> comes to match the target throttle opening amount TH*. Moreover, the engine ECU <b>24</b> uses the target throttle opening amount TH*, the speed Ne, and a preset map, not shown, and the like to obtain the fuel injection quantity at which the speed Ne can be quickly reduced by outputting torque from the motor MG<b>1</b> to the crankshaft <b>26</b>, while keeping the engine <b>22</b> firing to suppress degradation of the exhaust gas control catalyst <b>141</b><i>c</i>. The engine ECU <b>24</b> then executes fuel injection control to supply the obtained quantity of fuel to the combustion chambers <b>120</b>, as well as ignition timing control to keep the engine <b>22</b> firing. Also, after receiving the torque commands Tm<b>1</b>* and Tm<b>2</b>*, the motor ECU <b>40</b> performs switching control of the switching elements of the inverters <b>41</b> and <b>42</b> to drive the motor MG<b>1</b> according to the torque command Tm<b>1</b>* and drive the motor MG<b>2</b> according to the torque command Tm<b>2</b>*. Therefore, if the battery temperature Tb is equal to or lower than the reference temperature Tbref, the speed Ne of the engine <b>22</b> can be quickly reduced to the target speed Ne* (i.e., the self-sustaining speed Nref) while fuel continues to be supplied to the engine <b>22</b>, i.e., while the engine <b>22</b> is kept firing.

p-0042If, on the other hand, the determinations in steps S<b>140</b> and S<b>150</b> are yes but then it is determined in step S<b>160</b> that the battery temperature Tb input in step S<b>100</b> is above the reference temperature Tbref, a self-sustained operation command is output to the engine ECU <b>24</b> and the flag F described above is set to a value of 1 (i.e., step S<b>240</b>), and furthermore, the torque command Tm<b>1</b>* for the motor MG<b>1</b> is set to a value of 0 (step S<b>250</b>). Then steps S<b>190</b> to S<b>220</b> described above are executed, after which the target speed Ne* and the target throttle opening amount TH* are output to the engine ECU <b>24</b> while the torque commands Tm<b>1</b>* and Tm<b>2</b> for the motors MG<b>1</b> and MG<b>2</b> are output to the motor ECU <b>40</b> (step S<b>230</b>). Then this cycle of the routine ends. In this case, the battery temperature Tb exceeds the reference temperature Tbref, so in step S<b>190</b> the target throttle opening amount TH* is set relatively large compared to when the battery temperature Tb is relatively low (particularly when the battery temperature Tb is equal to or lower than the reference temperature Tbref).

p-0043After receiving the self-sustained operation command, the target speed Ne*, and the target throttle opening amount TH* from the hybrid ECU <b>70</b>, the engine ECU <b>24</b> controls the throttle motor <b>125</b> based on the throttle position obtained by the throttle valve position sensor <b>124</b> so that the opening amount of the throttle valve <b>123</b> comes to match the target throttle opening amount TH*. Moreover, the engine ECU <b>24</b> uses the target throttle opening amount TH*, the speed Ne, and a preset map, not shown, and the like to set the minimum amount of fuel that must be injected in order to keep the engine <b>22</b> firing to suppress degradation of the exhaust gas control catalyst <b>141</b><i>c</i>. The engine ECU <b>24</b> then executes fuel injection control to supply the set quantity of fuel into the combustion chambers <b>120</b>, as well as ignition timing control to keep the engine <b>22</b> firing. Also, after receiving the torque commands Tm<b>1</b>* and Tm<b>2</b>*, the motor ECU <b>40</b> performs switching control of the switching elements of the inverters <b>41</b> and <b>42</b> to drive the motor MG<b>1</b> according to the torque command Tm<b>1</b>* and drive the motor MG<b>2</b> according to the torque command Tm<b>2</b>*. In this case, no torque is output from the motor MG<b>1</b> to the crankshaft <b>26</b>, but in step S<b>190</b> as described above, the target throttle opening amount TH* is set large compared to when the battery temperature Tb is relatively low. Therefore, friction is increased by this setting of the target throttle opening amount TH*, i.e., the intake air adjustment, thereby promoting a decrease in the speed of the engine <b>22</b>. As a result, the speed Ne of the engine <b>22</b> is able to be quickly decreased to the target speed Ne* (i.e., the self-sustaining speed Nref) while fuel continues to be supplied to the engine <b>22</b>, i.e., while the engine <b>22</b> is kept firing.

p-0044In this way, after the flag F is set to a value of 1 in step S<b>240</b>, the determination in step S<b>140</b> thereafter, i.e., during the next cycle of the routine, will be no, so steps S<b>240</b>, S<b>250</b>, and S<b>190</b> to S<b>230</b> will be executed. Also, if the battery temperature Tb is equal to or lower than the reference temperature Tbref such that steps S<b>170</b> to S<b>230</b> described above are executed, and it is determined in step S<b>150</b> thereafter, i.e., during the next cycle of the routine, that the absolute value of the difference between the speed Ne of the engine <b>22</b> and the target speed Ne* is equal to or less than the predetermined value α and the speed Ne substantially matches the target speed Ne*, then steps S<b>240</b>, S<b>250</b>, and S<b>190</b> to S<b>230</b> will be executed.

p-0045As described above, with the hybrid vehicle according to this first example embodiment, the engine <b>22</b>, the motor MG<b>1</b>, and the motor MG<b>2</b> are controlled such that torque based on the required torque Tr* is output to the ring gear shaft <b>32</b><i>a </i>and the speed Ne of the engine <b>22</b> is decreased to the preset self-sustaining speed Nref with the setting of the target throttle opening amount TH* that increases the intake air amount of the engine <b>22</b> as the battery temperature Tb increases (i.e., with the intake air adjustment) and the injection of fuel into the combustion chambers <b>120</b> (and the ignition of that fuel), when there is a demand to decelerate the ring gear shaft <b>32</b><i>a </i>by the driver releasing the accelerator pedal <b>83</b> while the catalyst degradation suppression flag Fc is set to a value of 1 and a fuel cut in the engine <b>22</b> is being prohibited to suppress degradation of the exhaust gas control catalyst <b>141</b><i>c </i>(steps S<b>170</b> to S<b>250</b>).

p-0046That is, with the hybrid vehicle <b>20</b> according to the first example embodiment, when the battery temperature Tb is equal to or lower than the preset reference temperature Tbref when there is a demand to decelerate the ring gear shaft <b>32</b><i>a </i>while the catalyst degradation suppression flag Fc is set to a value of 1 and a fuel cut is being prohibited, the engine <b>22</b> and the motors MG<b>1</b> and MG<b>2</b> are controlled such that torque based on the required torque Tr* is output to the ring gear shaft <b>32</b><i>a </i>and the speed Ne of the engine <b>22</b> decreases to the self-sustaining speed Nref with the output of negative torque from the motor MG<b>1</b> to the crankshaft <b>26</b>, the setting of the target throttle opening amount TH* in step S<b>190</b>, and the injection of fuel into the combustion chambers <b>120</b> (and the ignition of that fuel) (step S<b>170</b> to S<b>230</b>). As a result, if the battery temperature Tb is relatively low such that the input limit Win of the battery <b>50</b> is not limited to a small amount of charge electric power by the relationship with the battery temperature Tb, the motor MG<b>1</b> is made to function as a generator, so the speed Ne of the engine <b>22</b> can be quickly decreased by outputting negative torque from the motor MG<b>1</b> to the crankshaft <b>26</b>.

p-0047On the other hand, if the battery temperature Tb is above the reference temperature Tbref when there is a demand to decelerate the ring gear shaft <b>32</b><i>a </i>while the catalyst degradation suppression flag Fc is set to a value of 1 and a fuel cut is being prohibited, the engine <b>22</b> and the motors MG<b>1</b> and MG<b>2</b> are controlled such that torque based on the required torque Tr* is output to the ring gear shaft <b>32</b><i>a </i>and the speed Ne of the engine <b>22</b> is decreased to the self-sustaining speed Nref with the setting of the target throttle opening amount TH* that increases the intake air amount of the engine <b>22</b> as the battery temperature Tb increases, and the injection of fuel into the combustion chambers <b>120</b> (and the ignition of that fuel), without outputting torque from the motor MG<b>1</b> (steps S<b>240</b>, S<b>250</b>, and S<b>190</b> to S<b>230</b>). Therefore, even if the speed Ne of the engine <b>22</b> stops being decreased by the motor MG<b>1</b> taking into account the fact that the battery temperature Tb is relatively high such that the input limit Win of the battery <b>50</b> is limited to a small amount of charge electric power by the relationship with the battery temperature Tb, it is still possible to promote a decrease in the speed of the engine <b>22</b> by increasing the friction by the setting of the target throttle opening amount TH* (i.e., the intake air adjustment) in step S<b>190</b>. Therefore, with the hybrid vehicle <b>20</b> according to this first example embodiment, the speed Ne of the engine <b>22</b> can be quickly decreased regardless of the state of the battery <b>50</b>, when there is a demand to decelerate the ring gear shaft <b>32</b><i>a </i>while a fuel cut in the engine <b>22</b> is being prohibited to suppress degradation of the exhaust gas control catalyst <b>141</b><i>c</i>. This kind of control is extremely useful for quickly decreasing the speed Ne of the engine <b>22</b> particularly when the accelerator pedal <b>83</b> is released while the engine <b>22</b> is operating at a high load and high speed.

p-0048Also, in step S<b>190</b> in the first example embodiment, the target throttle opening amount TH* is set as the control amount of the throttle valve <b>123</b> using the speed Ne of the engine <b>22</b>, the battery temperature Tb, and a target throttle opening amount setting map (<figref idrefs="DRAWINGS">FIG. 7</figref>) as a restriction in which there is a tendency to increase the intake air amount as the speed Ne increases, and increase the intake air amount as the battery temperature Tb increases. As a result, it is possible to more accurately adjust the intake air when there is a demand to decelerate the ring gear shaft <b>32</b><i>a </i>while a fuel cut in the engine <b>22</b> is being prohibited to suppress degradation of the exhaust gas control catalyst <b>141</b><i>c</i>. However, the target throttle opening amount setting map is not limited to the map shown in <figref idrefs="DRAWINGS">FIG. 7</figref>. For example, the target throttle opening amount setting map may also be a map such as that shown in <figref idrefs="DRAWINGS">FIG. 9</figref>, in which there is a tendency to increase the intake air amount as the speed Ne increases without relying on the battery temperature Tb when the battery temperature Tb is equal to or lower than the reference temperature Tbref, and increase the intake air amount as the battery temperature Tb increases as well as increase the intake air amount as the speed Ne increases when the battery temperature Tb is above the reference temperature Tbref. That is, the intake air amount may be set based on the speed Ne of the engine <b>22</b> without using the battery temperature Tb when the battery temperature Tb is equal to or lower than the reference temperature Tbref and the speed Ne of the engine <b>22</b> is decreased with the output of negative torque from the motor MG<b>1</b> to the crankshaft <b>26</b>.

p-0049<figref idrefs="DRAWINGS">FIG. 10</figref> is a block diagram schematically showing a hybrid vehicle <b>20</b>B according to a second example embodiment of the invention. Incidentally, structural elements of the hybrid vehicle <b>20</b>B according to this second example embodiment that are the same as those of the hybrid vehicle <b>20</b> according to the first example embodiment will be denoted by like reference characters and redundant descriptions of those elements will be omitted. The hybrid vehicle <b>20</b>B shown in <figref idrefs="DRAWINGS">FIG. 10</figref> is provided with a clutch C<b>1</b> capable of selectively connecting and disconnecting the rotating shaft of the motor MG<b>1</b> to and from the sun gear <b>31</b> of the power splitting/combining device <b>30</b>. This clutch C<b>1</b> is driven by a hydraulic actuator, an electromagnetic actuator, or an electric actuator, not shown, that is controlled by the hybrid ECU <b>70</b>. In the hybrid vehicle <b>20</b>B provided with this kind of clutch C<b>1</b>, if the battery temperature Tb is equal to or lower than the preset reference temperature Tbref when there is a demand to decelerate the ring gear shaft <b>32</b><i>a </i>while the catalyst degradation suppression flag Fc is set to a value of 1 and a fuel cut is being prohibited, the engine <b>22</b> and the motors MG<b>1</b> and MG<b>2</b> are controlled such that torque based on the required torque Tr* is output to the ring gear shaft <b>32</b><i>a </i>and the speed Ne of the engine <b>22</b> is decreased to the self-sustaining speed Nref with the output of negative torque from the motor MG<b>1</b> to the crankshaft <b>26</b>, the same setting of the target throttle opening amount TH* as that in step S<b>190</b> described above, and the injection of fuel into the combustion chambers <b>120</b> (and the ignition of that fuel), just as in the hybrid vehicle <b>20</b> described above.

p-0050On the other hand, if the battery temperature Tb is above the reference temperature Tbref when there is a demand to decelerate the ring gear shaft <b>32</b><i>a </i>while the catalyst degradation suppression flag Fc is set to a value of 1 and a fuel cut is being prohibited, the clutch C<b>1</b> is controlled to disconnect the rotating shaft of the motor MG<b>1</b> from the power splitting/combining device <b>30</b>, and the engine <b>22</b> and the motors MG<b>1</b> and MG<b>2</b> are controlled such that torque based on the required torque Tr* is output to the ring gear shaft <b>32</b><i>a </i>while the speed Ne of the engine <b>22</b> is decreased to the self-sustaining speed Nref with the setting of the target throttle opening amount TH* that increases the intake air amount of the engine <b>22</b> as the battery temperature Tb increases (i.e., with the intake air adjustment) and the injection of fuel into the combustion chambers <b>120</b> (and the ignition of that fuel). Therefore, even if the speed Ne of the engine <b>22</b> stops being decreased by the motor MG<b>1</b> taking into account the fact that the battery temperature Tb is relatively high such that the input limit Win is limited to a small amount of charge electric power, it is still possible to both prevent the speed of the engine <b>22</b> from decreasing by disconnecting the rotating shaft of the motor MG<b>1</b> from the power splitting/combining device <b>30</b> and using the inertia of the rotating shaft of the motor MG<b>1</b>, and quickly decrease in the speed Ne of the engine <b>22</b> by increasing the friction by the kind of setting of the target throttle opening amount TH* (i.e., the intake air adjustment) described above. However, in the hybrid vehicle <b>20</b>B provided with the clutch C<b>1</b> described above, the intake air adjustment described above before and after the motor MG<b>1</b> is disconnected from the power splitting/combining device <b>30</b> by the clutch C<b>1</b> may also be omitted.

p-0051Incidentally, thus far an example embodiment of the invention has been described illustrating a case in which the driver has released the accelerator pedal <b>83</b> when the catalyst degradation suppression flag Fc is set to a value of 1. Of course, the invention may similarly be applied to both a case in which the driver has depressed the accelerator pedal <b>83</b> again and a case in which the driver has depressed the brake pedal <b>85</b>. Also, with the hybrid vehicles <b>20</b> and <b>20</b>B according to the first and second example embodiments, the ring gear shaft <b>32</b><i>a </i>that serves as the drive shaft is coupled to the motor MG<b>2</b> via the reduction gear <b>35</b> that reduces the rotation speed output from the motor MG<b>2</b> and transmits it to the ring gear shaft <b>32</b><i>a</i>. However, instead of the reduction gear <b>35</b>, a transmission may also be employed that has two speeds, such as Hi and Lo, or three or more speeds, and changes the rotation speed output from the motor MG<b>2</b> and transmits the changed rotation speed to the ring gear shaft <b>32</b><i>a</i>. Moreover, the hybrid vehicle <b>20</b> of the first example embodiment outputs the power of the motor MG<b>2</b> to the ring gear shaft <b>32</b><i>a </i>that is connected to the ring gear <b>32</b> of the power splitting/combining device <b>30</b>. However, the invention is not limited to this structure. That is, the invention may also be applied to a structure that outputs the power of the motor MG<b>2</b> to a shaft (e.g., a shaft that is connected to the wheels <b>39</b><i>c </i>and <b>39</b><i>d </i>in <figref idrefs="DRAWINGS">FIG. 11</figref>) other than the ring gear shaft <b>32</b><i>a </i>(i.e., the wheels <b>39</b><i>a </i>and <b>39</b><i>b</i>), as in a hybrid vehicle <b>20</b>C according to a third example embodiment of the invention shown in <figref idrefs="DRAWINGS">FIG. 11</figref>.

p-0052Incidentally, in the foregoing example embodiments, the engine <b>22</b> corresponds to an internal combustion engine. Also, the exhaust gas control apparatus <b>141</b> that includes the exhaust gas control catalyst <b>141</b><i>c </i>for purifying exhaust gas discharged from the engine <b>22</b> corresponds to an exhaust gas control apparatus. Also, the motor MG<b>1</b> that both inputs and outputs power corresponds to a first electric motor. Further, the power splitting/combining device <b>30</b> that is connected to the crankshaft <b>26</b> of the engine <b>22</b>, the rotating shaft of the motor MG<b>1</b>, and the ring gear shaft <b>32</b><i>a </i>that serves as the drive shaft, and inputs and outputs power that is based on the power input and output from and to two of these three shafts to the remaining shaft corresponds to a power distributing portion. Also, the motor MG<b>2</b> that outputs power to the ring gear shaft <b>32</b><i>a </i>corresponds to a second electric motor. Further, the battery <b>50</b> that supplies and receives electric power to and from the motors MG<b>1</b> and MG<b>2</b> corresponds to a power storage device. The hybrid ECU <b>70</b> that executes step S<b>120</b> in <figref idrefs="DRAWINGS">FIG. 5</figref> corresponds to a required torque setting portion. The combination of the hybrid ECU <b>70</b>, the engine ECU <b>24</b>, and the motor ECU <b>40</b> that control the engine <b>22</b> and the motors MG<b>1</b> and MG<b>2</b> such that torque based on the required torque Tr* is output to the ring gear shaft <b>32</b><i>a </i>and the speed Ne of the engine <b>22</b> is decreased to the preset self-sustaining speed Nref with the setting of the target throttle opening amount TH* that increases the intake air amount of the engine <b>22</b> as the battery temperature Tb increases (i.e., with the intake air adjustment) and the injection of fuel into the combustion chambers <b>120</b>, when there is a demand to decelerate the ring gear shaft <b>32</b><i>a </i>by the driver releasing the accelerator pedal <b>83</b> while the catalyst degradation suppression flag Fc is set to a value of 1 and a fuel cut in the engine <b>22</b> is being prohibited to suppress degradation of the exhaust gas control catalyst <b>141</b><i>c</i>, corresponds to a control portion. The throttle valve <b>123</b> that regulates the intake air amount corresponds to an intake air amount regulating portion. The combination of the crank position sensor <b>180</b> and the engine ECU <b>24</b> corresponds to a rotation speed obtaining portion. The temperature sensor <b>51</b> that detects the battery temperature Tb corresponds to a temperature obtaining portion. The clutch C<b>1</b> that selectively connects and disconnects the rotating shaft of the motor MG<b>1</b> to and from the sun gear <b>31</b> of the power splitting/combining device <b>30</b> corresponds to a connecting/disconnecting portion. The power splitting/combining device <b>30</b> that has the carrier <b>34</b> that is connected to the crankshaft <b>26</b> of the engine <b>22</b>, the sun gear <b>31</b> that is connected to the rotating shaft of the motor MG<b>1</b>, and the ring gear <b>32</b> that is connected to the ring gear shaft <b>32</b><i>a </i>that serves as the drive shaft, with these three elements being able to differentially rotate with respect to one another, corresponds to a planetary gear set.

p-0053However, the internal combustion engine is not limited to the engine <b>22</b> that outputs power by receiving a supply of hydrocarbon fuel such as gasoline or light oil. That is, the internal combustion engine may be another type of engine such as a hydrogen engine. The exhaust gas control apparatus may be any type of exhaust gas control apparatus as long as it includes an exhaust gas control catalyst for purifying exhaust gas discharged from the engine <b>22</b>. The first electric motor and the second electric motor are not limited to being synchronous motor-generators like the motors MG<b>1</b> and MG<b>2</b>, but may be another type of electric motor such as an induction motor. The power storage device is not limited to being a secondary motor like the battery <b>50</b>, but may also take another form such as a capacitor as long as it is able to supply and receive electric power to and from the electric motor. The required torque setting portion is not limited to a structure that sets the required torque based on the accelerator operation amount and the vehicle speed, but may take another form such as a structure that sets the required driving force based on only the accelerator operation amount, for example. The control portion may also take a form other than the combination of the hybrid ECU <b>70</b>, the engine ECU <b>24</b>, and the motor ECU <b>40</b>, such as a single electronic control unit, for example.

p-0054The invention is able to be used in the manufacturing industry of power output apparatuses and hybrid vehicles and the like.

p-0055While the invention has been described with reference to example embodiments thereof, it should be understood that the invention is not limited to the example embodiments or constructions. To the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the example embodiments are shown in various combinations and configurations, which are exemplary, other combinations and configurations, including more, less or only a single element, are also within the spirit and scope of the invention.